The device ("IP reading device") known from the aforementioned publication contains an He-Ne laser for producing a scanning beam which along a scanning beam path through a partially transparent mirror impinges on a deflecting mirror and is then focussed by a lens on a scanning location, past which the phosphor storage plate is moved by a coordinate table. The scanning beam produces at the point of the phosphor storage plate housing the scanning location a fluorescent radiation representing the stored information which following collimation by the focussing lens is reflected by the deflection mirror and by the partially transparent mirror and is focussed by a second lens in the aperture of a diaphragm, downstream of which a photomultiplier is arranged. The diaphragm is necessary to laterally distinguish the luminescence signal from the storage plate, thus increasing the resolution of the reading system.
Due to the relatively limited aperture of the focussing lens and the optical losses caused by the lenses and mirrors in the beam path of the reading beam and lastly due to the diaphragm itself, only a relatively small proportion of the fluorescent radiation arrives at the photomultiplier so that the ratio of the wanted signal to the unwanted signal at the output of the photomultiplier needs to be improved.